Duplicating ink



United States Patent Office 3,436,234 Patented Apr. 1, 1969 3,436,234 DUPLICATING INK Jack H. Terry, Pittsford, N.Y., and Ernest R. Mueller, Co-

lumbus, Ohio, assignors, by mesne assignments, to Xerox gorporation, Rochester, N.Y., a corporation of New ork N Drawing. Filed Apr. 29, 1965, Ser. No. 451,988 Int. Cl. C0911 11/10 U.S. Cl. 10620 3 Claims ABSTRACT OF THE DISCLOSURE A pressure transfer ink made up of two or more pigment particles of differing average particle sizes in a specific ratio range dispersed in a substantially solid pressure transferable vehicle including an adhesive resin in proportions sufiicient to attain maximum transferability without smudging and the transfer process of using the ink.

This invention relates to a pressure transfer duplicating technique and, more particularly, to an improved inking material particularly adapted for use therein.

Various techniques have been developed for making multiple copies of original documents by the transfer of a relatively dry imaging material or ink. Perhaps the most well known of these techniques involves the use of an ordinary sheet of carbon paper between the original and a copy sheet in a typewriter. As is well known, this technique of making duplicates of an original typed document suffers from many drawbacks. For example, the carbon paper itself is easily smudged and tends to dirty the hands and clothing of the operator. In addition, be cause the ink on the carbon paper must transfer readily from the paper sheet under the application of pressure, it also tends to smudge and spread on the duplicates producing fuzzy, illegible and nonpermanent images on the copy sheet. Generally, only a few copies are possible because it is extremely difficult to transmit the pressure of the typed character throughout the whole thickness of the sandwich formed by the carbon sheets and the copy papers so that the readability of those carbon copies most remote from the typed characters drops off drastically. It is also very laborious to make corrections on carbon copies, since each copy must be individually corrected.

In order to overcome the many difficulties inherent in the production of duplicates with carbon paper, outlined above, a number of duplicating techniques have been developed such as spirit duplicating, mimeograph, offset and the like. Although some of these techniques produce copies which are vastly superior to carbon copies, they are somewhat more expensive than the use of carbon paper for short runs, sometimes involve messy liquids, and require the preparation of a separate master apart from the original. Although duplicating techniques which utilize a master are capable of producing copies at a relatively low cost which is even competitive with carbon copies when a large number of copies are reproduced, the time required and cost of materials involved in producing a master with these processes requires that the master making cost be amortized over a large number of copies. In addition, present day duplicating techniques require a fairly large capital investment in equipment while no such investment is required in making carbon copies. Accordingly, these techniques become prohibitive in cost if they are used to produce less than about twenty copies. In summary then, it may be said that there is not available at the present time any process for making a relatively small number of duplicates of an original document with simple, inexpensive apparatus which is competitive in price and yet still superior in quality to carbon copies.

An extremely simple duplicating process for making copies from an original by pressure transfer is now pro posed. This technique involves typing the original with a ribbon bearing an ink which is specially adapted to the process, placing the original in face-to-face contact with a transfer sheet and pressing the two together as with a pair of rollers so as to transfer a portion of the original ink to the transfer sheet. After separation of the master and original, which leaves a portion of the original ink on each of these two members, the inked transfer sheet is pressed in face-to-face contact with the copy sheets so as to transfer a portion of the ink on the transfer sheet to each of these copy sheets and form a right-reading duplicate of the original on them.

Although similar duplicating techniques have been proposed as, for example, in German Patent No. 646,530 and U.S. Patent 3,122,094, pressure transfer duplicating techniques of this type have never become commercial because of the extremely severe requirements which this type of duplicating process placed on the ink. First of all, the ink must have good transfer properties under the high rates of shear applied to the ribbon during the original typing operation so that sharp, clear letters are produced on the original which will not spread or smudge to any appreciable extent. This alone is quite difficult because a much heavier coating of ink must be applied from the ribbon during the original typing operations so that adequate ink will be present on the original to carry out the duplicating process. In addition, a large portion of the ink once transferred to the original must be capable of being transferred under the much lower rates of shearing applied when the original is pressed in face-to-face contact with the transfer sheet and passed between a pair of pressure rollers. Then after a portion of the ink on the transfer sheet is retransferred by pressure to successive copy sheets by passing them between the pressure rollers in face-to-face contact with the transfer sheet, the copies produced must have high resolution and density, imperceptible smudging and little or no tendency for the ink to retransfer to the hands of a person picking up the copy. The problems inherent in the process are even more impressive when one considers the smudging which occurs with ordinary carbon papers in which the ink is only transferred once.

In order to avoid smudging and improve transfer properties, carbon paper inks have been formulated which include adhesive resins for the purpose of holding the pigment particles together as much as possible once the formulation has been transferred. Typical formulations employing these adhesives are described, for example, in U.S. Patents 1,800,561 and 2,589,306. Although these adhesives do tend to reduce smudging, they also tend to inhibit transfer so that only small amounts of them can be added even to the ink formulations used in carbon papers. If larger amounts are added the density of the image will drop off sharply. In pressure transfer duplicating the problerns involved in using adhesive resins are even more severe because of the great number of transfer steps involved in producing ten or fifteen duplicates of the original.

It is therefore an object of this invention to provide a novel ink formulation capable of producing duplicate copies by pressure transfer.

Another object of this invention is to provide an ink formulation for pressure transfer duplicating which is capable of producing originals and copies which are more smudge resistant.

A still further object of this invention is to provide an ink formulation for use in pressure transfer duplicating capable of producing originals and copies with good density and sharpness.

An additional object of this invention is to provide a novel ink formulation for pressure transfer duplicating 3 with good pressure transferability so that it can produce a relatively large number of copies.

Yet another object of this invention is to provide an ink formulation and process for its use which is both less complex and costly and capable of producing higher quality and more images than carbon copy duplicating.

It is also an object of this invention to provide an ink formulation for duplicating with very simple and inexpensive apparatus.

These and still other objects are accomplished in accordance with the present invention, generally speaking, by employing two or more pigments of differing average particle size in a pressure ink formulation and using these pigments in proportions so as to attain the maximum packing density for the particles in the ink. This ink is precoated on a typewriter ribbon to a weight of about 2-8 lbs. per ream and this ribbon is then used as an ordinary typewriter ribbon.

Maximum pigment packing in the ink vehicle is achieved by blending particles of at least two distinct sizes together in the vehicle in a ratio designed to produce minimum porosity between pigment particles in the ink. Generally speaking, the larger pigment particles should have a diameter at least about 10 times that of the smallest particles and preferably about 16 times the diameter of the smallest particles for best results, especially in a system in which only two particle sizes are employed. It is to be understood, of course, that when used throughout this specification and appended claims that particle size does not mean that every particle of a particular particle size has exactly that size, but, instead, that particles of the selected size have a mean particle diameter of about that size and that at least 90% of the particles are within the range of the mean diameter plus or minus 10%. Thus, for example, where it is indicated that a mixture of 25% of large 300 millimicron diameter particles and 75% of smaller 22 millimicron particles is employed in the pigment mix, than the mean diameter of 75% of the particles is about 22 millimicrons and 90% of the particles fall within the range from 19.8 to 26.4 millimicrons in diameter and 25% of the particles have a mean diameter of about 300 millimicrons and 90% of those particles fall within the range of from 270 to 330 millimicrons in diameter. In other words, if the plot were made of particle diameter versus frequency of occurrence for the pigment particle mix to be employed in the invention, two very distinct and fairly narrow peaks centering around the two mean particle diameters would quickly become apparent with the peak for the finer particles being approximately three times as high as that for the coarser particles in this binary system.

'In a preferred ternary system, which produces even higher density and more smudge resistant prints, particles of three distinct sizes are employed including a coarse particle size, a fine particle size and an intermediate size with the coarse and fine particle sizes being of the sizes as defined above in connection with the binary system and the medium particle size having a mean diameter ranging from about to about 8 times the mean diameter of the fine particle size. When optimum percentages of about 50% coarse particles, medium particles and 40% fine size particles are employed in the ternary system, the minimum porosity is reduced to about 22% based on the bulk volume of the system as compared to a minimum porosity of about 25% with optimum percentages of 25 coarse particles and 75 fine particles in the binary system.

A still denser packing of pigment particles may be achieved with 4 or even 5 different size pigment particles; however, it is generally found that the increase in density produced by adding additional different size pigments does not justify the additional expense involved and, furthermore, that it is difficult to maintain a relatively large size ratio between the various pigment sizes 4 when more than three are employed so that no improvement and even a decrease in packing density may occur. The optimum percentages of each size of pigment to use for maximum density will, of course, vary with the number of different sized pigments used and their particular sizes. However, techniques and calculations for determining maximum density with various sizes of particles are known and described in the literature especially in ceramics texts. See for example, Elements of Ceramics" by F. H. Norton, Addison-Wesley Publishing Co., 1952. As illustrated more fully in the examples which follow, it has been found that important improvement in density and smudge resistance in the ink are directly related to the packing density of the pigments.

Any suitable material may be used for the pigment in the ink formulations so long as the optimum amounts of selected sizes of pigments in a binary or ternary system is employed to provide maximum packing density. Typical pigments include red and black iron oxides, carbon black, coal fines and other carbonaceous blacks, barytes (barium sulfate), cadmium sulfide, chrome yellow (lead chromate), Prussion blue, benzidine yellow, toluidine toner, Hausa yellow G, halogenated indanthrone, methyl violet, alkali blue toner, phosphotungstic and phosphomolybdic acid lakes of dyes such as Malachite Green, Brillant Green, Victoria Blue, Rhodamine 6G, Rhodamine B, Brillant Blue, 6G, etc. and mixtures of any of the above pigments. It should be understood that the pigments of various sizes required for optimum packing density, may all be of the same material and that any one size of pigment may be composed of a mixture of two or more pigments.

A mix of the required particle sizes of pigments may be blended in any suitable pressure transfer ink vehicle. Total pigment concentration should run from about 30 to about 75 by weight of the total ink formulation and, preferably, from about 45 to about 65% by weight of the total ink formulation so as to provide high density and minimal smudging in the many copies that are made from the formulation. Although the 45 to 65% range produces the best results with respect to smudging and transferability to produce a large number of prints, good results can also be produced throughout the wider range.

The general nature of the invention having been described above, the following examples are given in more specific illustration thereof.

EXAMPLES I-III The pigments for three ink formulations are made up as follows. For Example I there is employed 52 parts by weight of black magnetic iron oxide having a mean particle diameter of 300 millimicrons. For Example II there is employed 13 parts by weight of the black iron oxide of Example I and 39 parts by weight of carbon black particles having a mean particle diameter of 22 millimicrons, and for Example III there is employed 26 parts by weight of the black iron oxide of Example I, 21 parts by weight of the carbon black particles of Example II and 5 parts by weight of coal fines having a mean particle diameter of millimicrons.

Each of these three pigment batches is then employed to make up a separate ink formulation as follows. First 30 parts by weight of a polysiloxane gum, marketed by the General Electric Co. under the tradename silicone gum SE-76, is dissolved in 300 parts by weight of xylene. Then in a separate container, 5 parts by weight of a microcrystalline wax, 2 parts by weight of beeswax and 8 parts by weight of Piccolastic A-5 (a polystyrene resin with a molecular weight of about 300 and a ring and ball melting point of 5 C. available from the Pennsylvania Industrial Chemical Co.) are heated to about 250 F. and blended for about 20 minutes. The silicone gum solution is then added to the hot melt and ground in a ball mill for about one hour. The dry pigment is then mixed in and roller milled until the pigment is well wetted. In the case of Examples II and III pigment formulations, the dry pigments are first mixed in the roller mill for about one hour to secure a uniform blend of the various pigment sizes. The ink formulation is then coated on polyethylene ribbon to a dry weight of about 7 lbs/ream after which the xylene is driven off by gentle heating.

The three ribbons are then used to type out an original on ordinary ofiice bond paper in the same typewriter. Each original is then placed in face-to-face contact with a sheet of commercial wax paper, such as Freshwrap, and passed between a pair of driven rollers set to apply 200 lbs./ lineal inch to the sandwich. In each instance this wax paper transfer sheet is then separated from the original and placed in face-to-face contact with another sheet of the same type of ofiice bond paper, and these two are then passed through the rollers again at the same pressure setting and peeled apart to yield a pressure transfer copy on the bond sheet. This process is repeated with the master and fresh sheets of copy paper until the desired number of copies is produced. The originals and copies from the ribbons of Examples I, II and III are then compared, and it is apparent that ribbons II and III produce originals and copies of higher reflection density than those produced with the Example I ink formulation. The originals and copies made from the ink formulations of Examples I-III are then compared for smudging by testing in a Sutherland ink rub tester, and it is found that for the same number of cycles approximately 50% additional weight is required to produce perceptible smudging in the Example II original and copies as compared with the weight required to produce smudging of the Example I original and copies employing the same number of rub cycles in each instance and an additional 10% weight increase is required to produce smudging with the original and copies made from the Example III formulation.

EXAMPLES IV-VI The procedure of Examples I-III is repeated using the same ratio of 52 parts by weight pigment to 48 parts by weight of vehicle but using a vehicle made up of 10 parts by weight of a microcrystalline wax, 4 parts by weight of beeswax, 8 parts by weight of Piccolyte S70 (a polyterpene made predominately from beta pinene and having a ring and ball melting point of 70 C.) and 8 parts by weight of petrolatum. In this instance no solvent is employed in the blending, and the pigments are blended directly into a hot melt of the vehicle component followed by roller milling to disperse them. Upon cooling of the three ribbons the imaging procedure described in Examples I-III is followed with roughly the same results except for the fact that smudging is higher in all instances apparently because of the softer consistency of the petrolatum component of the vehicle as opposed to the silicone gum employed in the vehicle of Examples I-III. Here again, the ink formulation employing only iron oxide pigments shows the highest degree of smudging with about a increase in weight required to produce smudging with the two-pigment formulation and about a increase to produce smudging with the three pigment formulation. Density is also increased visibly in the multipigment formulations.

EXAMPLES VII-IX 5 The procedure of Examples I-III is repeated with everything remaining the same except that non-magnetic iron oxide is substituted for iron oxide. No perceptible change over the results obtained in Examples I-III is noted.

EXAMPLES X-XII The procedure of Examples I-III is repeated with everything remaining the same except that various carbon blacks of the prescribed sizes are substituted for both the iron oxide and the coal fines. No perceptible change over the results obtained in Examples I-III is noted.

What is claimed is:

1. An improved duplicating ink consisting essentially of an adhesive resinous vehicle and pigment 30 to 75 percent by weight of said ink, the improvement comprising coarse pigment particles of a size ranging from about 270 millimicrons to about 330 millimicrons and fine pigment particles of a size ranging from about 19.8 millimicrons to about 26.4 millimicrons.

2. An improved duplicating ink according to claim 1 wherein said pigment comprises from about 45 to about percent by weight of said duplicating ink.

33. An improved duplicating ink consisting essentially of an adhesive resinous vehicle and pigment 30 to percent by weight of said ink, said pigment consisting essentially of large, medium and small size particles, a ratio between the mean diameter of said large particles to that of said small particles ranging of about 16 to l to about 10 to l, and the ratio of said medium size particles to that of said small particles ranging from about 8 to 1 to about 5 to 1, said large pigment particles ranging in size from about 270 millimicrons to about 330 millimicrons [medium pigment particles ranging from about millimicrons to about millimicrons] and small pigment particles ranging from about 19.8 millimicrons to about 26.4 millimicrons.

References Cited UNITED STATES PATENTS DONALD J. ARNOLD, Primary Examiner.

J. B. EVANS, Assistant Examiner.

US. Cl. X.R. 

